A gas turbine combustion chamber in which premixed combustion takes place is provided with a pilot burner for combustion in addition to the main burners for premixed combustion. The pilot burner serves to stabilize the combustion. The diffusion flame or premixed flame produced by the pilot is used as the pilot flame for the main burner in order to produce a more fuel-rich flame, which stabilizes the combustion. If necessary, a pilot burner can have a cone at the outlet, which facilitates the stabilization of the pilot flame. In such a gas turbine combustion chamber the main burners are arranged at regular intervals around the pilot burner. High performance of such a gas turbine combustion chamber demands high turbine inlet temperatures which result from a high flame temperature. With regard to the development of CO and NOx values, it is necessary to maintain the flame temperature and the dwell time of the gas in the combustion chamber within a permissible range.
The high temperatures in the gas turbine demand a high flame temperature, which also have an effect on the NOx values and increase these values. However, in order to maintain the NOx values within the permissible range, the mean flame temperature in the combustion chamber should be minimized to a permissible value that is adapted to the efficiency, with respect to the developed NOx values. In addition, it would be necessary to reduce the dwell time of the gas in the combustion chamber, for example by means of a shortened combustion chamber.
However, for low NOx values it is likewise necessary to achieve low CO values. However, the CO values increase at a flame temperature of below 1300° C. Locally restricted volumes in the combustion chamber in which temperatures fall below this lower temperature limit can also have a dominant effect on increased emissions of CO. In order to keep CO to a low value, good intermixing is necessary. However, for this it is necessary to increase the dwell time or the mixing length of the gas in the combustion chamber, for example by lengthening the combustion chamber. However, this is in contradiction to a shortening of the dwell time for reduction of the NOx values.
Furthermore, however, in order to maintain the NOx values within the permissible range, measures could be taken, for example preheating or even reducing the compressed air which is fed to the combustion chamber, or even modifying the supply system, at least partially, in order to direct it around the combustion chamber. This would, however, have a detrimental effect on the operation of the turbine under base load. In addition, manufacturing costs would increase as a result. Moreover, the availability of the machine could be restricted, which likewise would be a serious disadvantage.